Acoustic diaphragm



L. STEVENS ACOUSTIC DIAPHRAGI Fil ed April 5, 1927 Sept. 24, 1929.

0P INVENTOR. BY g i ATTORNEY Patented Sept. 24, 1929 UNITED STATES LESLIE STEVENS, OF GLEN RIDGE, NEW JERSEY, ASSIGNOR TO STEVENS EANUFAG- TUBING CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE ACOUSTIC DIAPHRAGM Application filed April 5, 1927. Serial No. 181,028.

r This invention relates to acoustic diaphragrns and methods of making the same. The object of the invention is to rovide an improved large, direct-acting diap ragm, requlring no horn or other sound amplifying device, es ecially intended for use in radio loud spea (ers, but also adapted for use as a honograph reproducer, and as a sound col ecting diaphragm for radio transmitting 1o apparatus or phonograph recording apparatus.

A diaphragm according to the invention is a seamless diaphragm made from a contmuous piece of on'e'or more layersof plies, usually two, of woven fabric impregnated with stifi'ening material and stretched and deformed, without folds or laps, to the desired shape while the stifiening material is moist, and held stretched in the shape to which -it has been deformed until the stiffening material has become set. The diaphragm is usually made of bulging or dished form, most desira 1y conical, and better conoidal and continuously curved from its center outward in radial directions'rather than of'true cone form, and is shaped by bein pulled and tensioned against a form whic may be heated to secure quick dryin and setting of the stiffen-ing material. 'I he interstices of the fabric are filled to make the diaphragm impervious to air, or substantiall so, either b using for application to the fabric before it is shaped a stiffening material of a character to serve this purpose, or, and most desirably, by applying to the shaped diaphragm a coat- 1 ing of filling material which also serves to increase the stiffness and resiliency of the diaphragm and to make it water proof. The die hragm may be made of very light weight an ofsuch degree of flexibility and resiliency' as to be highly responsive to sound vibrations. It is very durable and not easily injured as compared to the paper cone-shaped diaphragms commonly used' for radio loud speakers and phonograph reproducers', and it is not affected by atmosphere moisture.

In the accompanying drawings, Figs. 1, 2 and 3 are sectional views of illustrative diaphragms according to the invention.

Fig, 3 is a sectional view on a. larger scale of a part of a diaphra m of the shape of the diaphragnrishown in ig. 3, made of two plies or layers of fabric.

Fig. 4 is a sectional view of a form for shaping diaphragms such as shown inFig. 1, and a cooperating clamping ring and parts of a press in which the form and clamping ring are mounted.

I igs. 1 and 2 show diaphragms of conoidal 50 form, the main portion of the diaphragm be-. ing continuously curved from the center of apex outward in radial directions; the diaphragm shown in Fig. 1 bein convexly curved and that shown in Fig. 2 %eing con- 55 oavely curved. Fi 3 shows a diaphragm of true cone sh'ape. hen the diaphragm is mounted with its periphery unsupported, that is, when mounted to operate as a free edge diaphragm, it is desirable that it be formed at or adjacent to its peripheral edge with a circumferentialcorru tion, or reverse bend .flange, as shown in Figs. 1 and 2. This -corrugation stiflens the edge of the ,diaphragm and aids in maintaining the diaphragm in shape and increases the definition of sound reproduction when the diaphragm is mounted with its edge free, Y

The conical diaphragms shown in Figs. 1, 2 and3 are to be understood as only illustrag tive of the many forms to which the diaphragms according,tothe'invention may be shaped. They may be made of various other conoidal shapes and other sha es in which the fabric is deformed from t e plane of its 35 Weave, such deformation of the fabric being accomplished by stretching the fabric, which is then held under tension in the shapeto which it has been stretched untilthe sizing or stiffening material with which the fabric is no impregnated has become set.

The shaping apparatus illustrated in Fig. 4 comprises a metal form 10 shown as shaped to form a diaphragm such as shown by Fig. 1, in which, as in the diaphragms shown in Fi s. 2 and 3, the central portion a of the materlal is displaced from the plane of its peripheral portion b and intermediate portions 0 extend at an angle to said plane. The form 10 is mounted on the bed plate 11 of any suitable press having an upper member 12, and means for causin an approaching movement between the ed plate 11 and such upper mem-' ber, usually by downward movement of the upper member. The upper member or cross head 12 of the press carries depending therefrom a clampin ring 13 which is formed to cooperate wlth t e peripheral portion of the form 10. The form 10 and the clamping ring 13 are shaped to form a circumferential corrugation such as shown in Fig. 1, near the edge of the diaphragm, the form for this purose being rovided with a circumferential emf 14 an the clamping ring witha corresponding circumferential channel 01:.recess 15. The form and the clamping ring are most desirably heated, as by means of a rin bumer 16 for heating the form and a ring urner 17 for heating the clamping ring.

In making a diaphragm in accordance with the invention, using shaping apparatus such as shown in Fi 4 for shaping t e diaphragm, the rocedure 1s as follows.

T e fabric to be used is most desirably flat woven plain cross-weave fabric of cotton or other suitable material, although other woven fabric might be used. The term woven fabric is intended to include fabric known as knitted or crocheted fabric, although a knittedor crocheted fabric is not ordinarily so desirable as a plain cross-weave fabric. The 1piece of fabric to be used in making the diap ragm may be a single sheet or layer or ma be of several sheets or layers laid toget er, the number of layers, one or more, depending on the weight of the fabric used, and the desired weight or thickness of the diaphragm. I have usually found it most desirable to make the diaphragms of two plies or layers ofrather thin o en-mesh cotton fabric,one layer being of e net and the other of a somewhat closer woven cloth such as 6r resembling cheese cloth. Such a two-ply diaphragm is illustrated by Fig. 3. The piece of fabric, whether of one or more layers, is a continuous piece, that is, without any cut or slit therein. The fabric before being sha d has applied thereto suitable sizing or sti ening material, such as a solution of starch or water-soluble lue. Usuall the fabric is sized, or treate with the sti ening material,

and allowed to dry. Then, before shaping, the piece of fabric 1s dampened sufliciently to soften but not to wash out the stifienin material.- The iece of fabric is then place on the shaping for 10, which is heated to a suitable temperature, most desirabl about 200 F., and the material is then u led out smoothly over the form, all wri les being pulled out, and while i is held'stretched over the form the press is operated to lower the clamping ring to clamp the edge of the material against the peripheral portion of the form and to shape the circumferential cor- 5 rugation. The diaphragm is then left clamped on the form until the moisture has dried out and the stiffening material is set. It is then removed from the form. When removed from the form the diaphragm is stiff enough to retain its shape, the stifi'ened fabric being flexible and resilient.

The stifiening material which I find it most desirable to use for appl ing to the fabric before sha ing the diaphragm does not make the dia liragm as stifi as it desirably should be, t e interstices of the fabric are not filled and the diaphragm is more or less pervious to air and not suitable for use as an acoustic diaphragm, and it will not stand exposure to moist atmos here. The diaphragm is therefore additionally treated to further stifl'en it, to fill the interstices of the fabric, and to render it waterproof. This is accomplished most desirably b the application to both sides of the diap ragm of a coating of filling and stiffening and waterproofing material consisting of a quick-drying liquid binding agent containing a metallic powder. The binding agent which I have found most suitable 1s a nitro-cellulose lacquer consisting of nitro-cellulose dissolved in amyl acetate with a small percentage of gum or wax to keep it from becoming brittle when dried, and a suitable mixture is formed by adding about one half ounce of aluminum powder or one ounce of bronze powder to two ounces of the solution. This mixture may be brushed or sprayed on to the diaphragm and this should be done as soon as ossible, or before the shaped diaphragm as been exposed for any considerable length of time to a moist atmosphere. The powder in the mixture held by the binding agent serves as a filler for the interstices 1n the fabric, and the binding agent adds stifi'ness to the diaphra and roofs it against moisture. By applymg-asu cient- 'ly heavy coating of the lacquer or other stiffening1 and water-proofing material to the dia ragm, the interstices in the fabric may be led without the use of insoluble powdered material added to the lacquer, but this is not usually desirable for the reason that the heavy coating required adds substantiall to the weight of the diaphra Powdered material other than met 'c powder might be used, but the metallic powder seems to ave the advantage of increasing the resiliency of the diaphragm. The use of powdered aluminum 1s especially desirable because of its com aratively light weight and also ap arently cause of other characteristics of this metal.

The filling and further stiffening material should be applied to the diaphragm before the sizing, or stifiening material, which is applied to the fabric before it is shaped has been allowed to become softened through exposure to moist atmosphere, and the latter applied material should be of such chara'cter that it will'not itself'act to soften the sizing. frisstatem'thesizing, or first applied stifi'enin material, is most desirably a wa- "ter solu b1'e material, and in order to avoid the softening of this materialby the later applied filling and stiifenin material, this latter material should be ma e with a solvent which does not readily dissolve the sizing, or should be'a quick-drying liquid, and may desirably'have'both of these characteristics.

An open mesh, rather than a close or tightwoven fabric, is'used because of its being more ada table to being deformed from the plane of i s weave having its warp and woof strands displaced from their normal relation, and also because of its being more freely pervious to, air with the sizing applied thereto than a close-woven fabric. When the fabric is beingstretched over the form, pocketing of air between the form and the fabric would prevent the fabric from coming accurately to shape against the whole surface of the form. As it is most desirable to use a form having a smooth impervioussurface, such pocketing j'of air isbest avoided by having the fabric freely pervious when being shaped on the form. Therefore, not only should a comparatively open mesh fabric be used, but the sizing or filling material a plied to the unshaped fabric should be suc as not to make the fabric impervious to air, a filling material being applied after the fabric has been shaped to fill the interstices of the fabric and make the diaphragm impervious to air or sub- 1 stantiallyso.

The diaphragms may be made of practically any size to act directly with the surrounding air without requiring the use of a horn or other sound amplifying means when the diaphragm is used for sound reproduction or as a sound concentrating means when the diaphragm is used for sound recording, and the shape to which the diaphragms are formed may vary widely from those shown. The diaphragms have usually been made round, and from 9 inches to 21 inches in diameter, but they may be made larger than 21 inches in diameter or somewhat smaller than 9 inches in diameter. The size of the diaphragm, as is 'well known, has an effect on the quality of sound reproduction. Diaphragms of conical shape havebeen found In the stretchin anddeforming of the fabric in shaping t e diaphragm, the fabric is pulled into the desired shape without any folding, or lapping, of any parts thereof which are to form part of the diaphragm. and it is put under tension in all directions and is held under such tension until the sizing or stiffening material with which the fabric is impregnated has become set. The result is that the fabric, woven from strands of cotton or other material having some degree of elasticity, is held under tension by the stiffening material, which in turn must be under some degree of compression caused by the tension of the strands of the fabric. This, together with the characteristic elasticity of the stiffening material, causes the diaphragm to have a high degree of elasticity or resiliency. In addition to this characteristic of being highly resilient,'the diaphragm, as stated, may be made of very light weight and of any desired degree of flexibility, and as a result of these characteristics diaphragms according to my invention are very eflicient for sound reproduction, both in the matter of loudness and quality of reproduction.

What is claimed is:

1. The method of making large, directacting, acoustic diaphragms of conical form, which comprises stretching a continuous piece of fiat-woven fabric impregnated with stiffening material in a moist condition over a form to shape the fabric without lapping and to tension it in all'directions, holding the fabric stretched on the form until the stiffening material has become set, and thereafter applying to the diaphragm material to fill the interstices in the fabric and to waterproof and further stiffen "the fabric.

2. The method of making large, directacting, acoustic diaphragms, which comprises stretching a continuous piece of woven fabric impregnated with a water-soluble stiffening material in a moist condition over a form to shape and tension the fabric without lapping, holding the fabric stretched on the form until the stifienin material has become set,-and applying to 0th sides of the diaphragm'a'coating of quick drying, filling 1 and waterroofing material to fill the interstices of t e fabric and to make the diaphragrii resistant to atmospheric moisture.

3. The method of making large, directacting, acoustic diaphragms, which comrises stretching a continuous piece of woven abric impregnated with stiffening material in a moist condition over a form to shape and tension the fabric without lapping, holding the fabric stretched on the form ,until the stifl'ening material has: become set, and applying to the diaphragm a coating of ma terial comprising a binding solution and a metallic powder.

4. The method of making-large, directacting, acoustic diaphragms of conical form, which comprises stretching a continuous piece of woven fabric impregnated with stifl'enin material in a molst condition to deform t e fabric from the plane of its weave to the desired shape of the diaphragm, and holding the fabric stretched in the shape to which it has been deformed until the stifl'ening material has become set.

5. The method of making large, direct acting, acoustic diaphragms, which comprises stretching a continuous piece of flatwoven fabric impregnated with stifl'ening material in a moist condition and deforming it from the plane of its weave to the desired shape of the diaphragm, holding the fabric stretched in the shape to which it has been deformed until the stiffening material has become set, and thereafter applyin material to the diaphra m to fill the interstices in the fabric and to urthcrstifl'en the fabric.

6. A seamless and lapless large, directacting, acoustic diaphragm consist-in of a continuous piece of stretched fabric deformed out of the plane of weave, the fabric being impregnated with stiffening material which imparts stiffness and resiliency to the fabric.-

7. A seamless and lapless large, directacting, acoustic diaphragm consisting of a continuous piece of stretched woven fabric deformed out of the plane of weave, the fabric being under tension and being impregnated with elastic stiffening material.

8. A seamless and lapless, large, direct-acting, acoustic diaphragm, consisting of a continuous piece of stretched woven fabric having its central ortion displaced from the plane of its perip eral portion and with intermediate portions extending at an angle to said plane, the fabric being under tension and bein impregnated with stiffening material whic stilfens the fabric and renders 1t resilient.

9. A seamless and laplcss, large, direct-acting, acoustic diaphragm, consistin of a continuous piece of stretched woven fabric having its central portion displaced from the plane of its peripheral portion and with intermediate portions extending at an angle to said plane, the fabric being under tension and bein impregnated with a stiffening material whlch stifl'ens the fabric and renders it .resilient, and having applied thereto a coattermediate portions extending at an angle to said plane, the fabric being treated with stiffening and filling material which stiifens the fabric and renders it resilient and fills the interstices thereof.

11. A seamless large, direct-acting, aeoustic diaphargm, consisting of a continuous.

- portions exten ing at an angle to said plane,

the fabric being impregnated with a still'cning material which stifi'ens the fabric and renders it rcsilient, and having metallic aluminum applied thereto in quantity snflicient lo fill the interstices of the fabric and held by a binding agent.

13. A seamless, large direct-acting, conical acoustic diaphragm, consisting of a continuous piece of stretchcd wovcn fabric, thwfabric being stiffened and held in shape and rendered resilient by an impregnating stiffening material.

14. A seamless large, direct-acting, conical acoustic diaphragm, consisting of a continu-' ous piece of stretched woven fabric, the fabric having applied thereto an elastic stiffening and filling and water-proofing material some of which impregnates the fabric.

15. A large, direct-acting, conical acoustic diaphragm, consisting of a continuous two layer )lOCB of stretched woven fabric, the fabric eing stitl'ened and held in shape and the layers of the fabric being cemented to gethcrby impregnating stilfening material.

16. A large, direct-acting acoustic liaphragm, consisting of a continuous piece of stretched flat-woven fabric comprising a plurality of layers of different mesh deformed out of the plane of weave, the fabric being stiffened and held in shape and the la ers of the fabric being cemented together y impregnating stiffening material.

hragm, consisting of stretched woven fabric old in shape by stiffening material and having a filling of powdered metal.

In testimony whereof I have hereunto set my hand.

LESLIE STEVENS.

17. A large, direct-acting, acoustic dia 

